FR vs FR-LSH
vs LSZH.
FR stands for Flame Retardant (IS 694:2010). FR-LSH, also written FRLSH, stands for Flame Retardant Low Smoke and Halogen (IS 694:2010): HCl emission up to 20%, smoke density rating up to 60%. LSZH stands for Low Smoke Zero Halogen, also sold as FR-LSZH or FRLSZH (Flame Retardant Low Smoke Zero Halogen); its BIS designation is HFFR, Halogen-Free Flame Retardant (IS 17048:2018): HCl emission up to 0.5%, light transmittance through smoke at least 70%. Three cable types. Three performance levels. This guide gives the test limits in each standard, what NBC 2016 says about each type, and where each is typically specified.
The three types — at a glance.
What "FR" and "LSH" and "LSZH" actually mean in measurement.
These are not marketing terms — they are defined test limits in Indian and international standards. Every test limit below is taken from IS 694:2010 and IS 17048:2018. Conductor temperature is the rating of the National Cables range.
| Test Parameter | FR (IS 694:2010) | FR-LSH (IS 694:2010) | LSZH/HFFR (IS 17048:2018) | Standard |
|---|---|---|---|---|
| Oxygen Index (OI) | ≥ 29% | ≥ 29% | ≥ 31% (thermoplastic) | IS 10810 (Part 58):1998 |
| Temperature Index (TI) | ≥ 250°C | ≥ 250°C | ≥ 250°C (thermoplastic) | IS 10810 (Part 64):2003 |
| Halogen acid gas (as HCl, by weight) | Not specified | ≤ 20% | ≤ 0.5% (fluorine ≤ 0.1%) | IS 10810 (Part 59) |
| Acidity of combustion gases | Not specified | Not specified | pH ≥ 4.3, conductivity ≤ 10 µS/mm | IS 17048:2018 Annex D |
| Smoke | Not specified | Smoke density rating ≤ 60% | Light transmittance ≥ 70% | FR-LSH: IS 13360 (Part 6/Sec 9) · HFFR: IS 10810 (Part 63) |
| Flammability | Burning ≤ 60 s after flame removal | Burning ≤ 60 s after flame removal | Burning ≤ 60 s after flame removal, plus flame retardant test | IS 10810 (Part 53) · HFFR also Part 61 |
| Max conductor temperature | 70°C | 70°C | 70°C | IS 694:2010 / IS 17048:2018 |
| BIS standard | IS 694:2010 | IS 694:2010 | IS 17048:2018 (separate licence) | BIS |
FR-LSH permits HCl up to 20%. LSZH/HFFR permits HCl up to 0.5%. That is a forty-fold difference in the permitted halogen limit. A BOQ or drawing that specifies IS 17048:2018 HFFR cannot be satisfied by IS 694:2010 FR-LSH. They are separate BIS standards with separate licence requirements. Always check which standard is specified — they are different products, not different names for the same thing.
National Cables selection guidance by building zone.
NBC 2016 Part 8/Sec 2 cl. 5.3.7.1 states that it is desirable to use flame retardant cables and wires in electrical distribution systems. The same clause notes that FR-LSH cable is available and may be considered. NBC 2016 Part 8/Sec 2 cl. 2.1.15 and 2.1.16 define FR and FR-LSH cable by reference to IS 694:2010. IS 17048:2018 is not cited in NBC 2016. The table below is National Cables selection guidance, not a code requirement. The project specification governs.
| Building / Zone | Suggested Cable | Why |
|---|---|---|
| Back-of-house, plant rooms, external runs | FR IS 694:2010 | Non-occupied zones — basic flame retardance sufficient |
| Corridors, escape routes, lift lobbies | FR-LSH IS 694:2010 | Evacuation routes — smoke must not impair visibility |
| Occupied floors — offices, residential | FR-LSH IS 694:2010 | People present — low smoke protects evacuation |
| High-rise buildings — all areas | FR-LSH IS 694:2010 | Vertical escape routes — low smoke protects evacuation |
| Hospitals — all wiring | HFFR IS 17048:2018 | Patients cannot self-evacuate — smoke is the primary hazard |
| Hotels — 5-star, all occupied areas | FR-LSH IS 694:2010 | Dense occupancy, sleeping accommodation |
| Schools, colleges, places of assembly | FR-LSH IS 694:2010 | Public buildings — high occupant density |
| Underground metro stations | HFFR IS 17048:2018 | Underground enclosed, limited exit |
| Airport terminal buildings | HFFR IS 17048:2018 | Dense passenger occupancy |
| Data centres, server rooms | HFFR IS 17048:2018 | Equipment survival — HCl gas corrodes servers at sub-ignition temperatures |
The fire safety case for FR-LSH and HFFR — in plain numbers.
In most building fires, occupants are incapacitated by smoke before they reach flame. Toxic HCl gas impairs coordination and consciousness before it causes direct injury. The rationale for FR-LSH and HFFR is not primarily about the cable burning — it is about what the cable releases when it burns near other burning materials.
IS 694:2010 sets no smoke limit for plain FR cable. FR-LSH must not exceed a smoke density rating of 60% (IS 13360 Part 6/Sec 9). HFFR must allow at least 70% light transmittance through its smoke (IS 10810 Part 63). The two tests use different methods, so the figures are not directly comparable.
Specify by product — the three types in the National Cables range.
FR Single Core Wire — flame-retardant PVC, IS 694:2010. FR-LSH Single Core Wire — flame retardant, low smoke and halogen, IS 694:2010. LSZH / HFFR Wire — halogen-free flame retardant, IS 17048:2018. All three ranges use Class 5 conductors — strand construction and resistance limits: IEC 60228 / IS 8130:2013 conductor classes. Size selection for a given load: cable size calculator.
Pairwise comparisons: FR vs FR-LSH · FR vs LSZH · FR-LSH vs LSZH.
FR vs FR-LSH vs LSZH — selection questions.
How to decide which insulation family is correct for a specific building zone or application.
What is the full form of FRLSH and FRLSZH?
FRLSH (FR-LSH) stands for Flame Retardant Low Smoke and Halogen. It is PVC-based cable to IS 694:2010, with HCl emission ≤ 20%.
FRLSZH (FR-LSZH) stands for Flame Retardant Low Smoke Zero Halogen. It is the same category as LSZH and HFFR (Halogen-Free Flame Retardant), made to IS 17048:2018, with HCl emission ≤ 0.5%. Plain FR stands for Flame Retardant (IS 694:2010), with no HCl limit.
Is FRLSH halogen-free?
No. The "H" in FR-LSH means low halogen, not zero halogen. IS 694:2010 permits FR-LSH HCl emission up to 20%.
Halogen-free cable is HFFR / LSZH to IS 17048:2018, which limits HCl to 0.5%, a 40-fold difference. The two are separate BIS standards with separate licences, and one cannot be substituted for the other in a BOQ.
Can I substitute FR-LSH (IS 694:2010) for HFFR (IS 17048:2018) in a hospital?
No. Both are flame retardant, but the HCl emission limits are not interchangeable: FR-LSH permits up to 20% HCl per IS 694:2010, while HFFR permits up to 0.5% per IS 17048:2018 — a 40-fold difference.
NBC 2016 does not mandate HFFR for hospitals, and IS 17048:2018 is not cited in NBC 2016. Specify HFFR to IS 17048:2018 where the project specification limits halogen acid gas to 0.5%. Where a hospital BOQ names IS 17048:2018, FR-LSH to IS 694:2010 does not meet it.
Is plain FR sufficient for a residential building?
Plain FR (IS 694:2010) has the flame retardant property that NBC 2016 Part 4 cl. 3.4.6.1 describes as desirable for wiring and cabling. NBC 2016 does not set cable type by storey count.
NBC 2016 Part 8/Sec 2 cl. 5.3.7.1 notes that FR-LSH cable is available and may be considered. National Cables suggests FR-LSH (IS 694:2010) for escape routes and for all areas of high-rise residential buildings. The project specification governs the cable type.
Why is LSZH/HFFR specified for data centres and metros if FR-LSH meets the smoke limit?
Data centres and metro stations specify HFFR (IS 17048:2018) primarily because of HCl gas damage to equipment, not just occupant safety. Burning PVC insulation — whether FR or FR-LSH — releases hydrogen chloride gas that corrodes electronic circuits, contacts, and metal infrastructure even at sub-ignition temperatures.
HFFR's ≤ 0.5% HCl limit (versus ≤ 20% for FR-LSH) protects equipment survival during a fire elsewhere in the building. For data centres, this can mean the difference between recoverable infrastructure and a total write-off. Underground metro stations carry the additional concern of evacuation in a confined space.
Are LSZH and HFFR the same product, or two different categories?
LSZH (Low Smoke Zero Halogen) and HFFR (Halogen-Free Flame Retardant) describe the same product category — both compliant with IS 17048:2018. "HFFR" is the formal BIS designation; "LSZH" is the colloquial term emphasising the low-smoke and halogen-free properties. The "zero" in LSZH is approximate — IS 17048:2018 permits HCl ≤ 0.5%, not strictly zero.
What matters operationally: ensure the cable carries a valid IS 17048:2018 BIS licence (separate from any IS 694:2010 licence) and meets the limits — Oxygen Index ≥ 31% (thermoplastic), light transmittance ≥ 70%, HCl ≤ 0.5%.
Specify the correct cable for your project.
Our technical team matches IS 694:2010 and IS 17048:2018 cable types to your project specification.